The development of late Holocene coastal cooling in the northern South China Sea

Paired high-resolution sea surface temperature (SST) records, based on the long-chain alkenone unsaturation index (U-37(K)'), were reconstructed to decipher the SST evolution over the past 8000 years and its possible driving mechanisms at the Hong Kong coastal region. The two SST records, derived from a sediment core in the Pearl River Estuary and an offshore core in the northern South China Sea (SCS), show different patterns of SST changes. The coastal record shows relatively stable, warm temperatures during the mid-Holocene (similar to 7.4-2.6 ka), and substantial cooling (>2 degrees C) thereafter. The cooling was most pronounced in the past similar to 0.6 ka, likely associated with the Little Ice Age (LIA). The offshore record generally reveals a warming trend from 8 ka to similar to 3.5 ka and relatively warm temperatures since then. As a result, the SST difference (Delta SST) between the two sites increased over time, suggesting that the SST gradient gradually developed in the northern SCS. The declining coastal SST with the increasing DSST likely indicates and results from the intensified East Asian winter monsoon since similar to 7 ka, especially during the late Holocene. Consistent with previous terrestrial records revealing winter monsoon variability and modern observations, Delta SST between coastal and offshore sites could thus be used as an indicator of winter monsoon variability. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.